Wednesday, March 4, 2009

Where is My Ride?

Sorry for the long delay in reporting from the technology fronts. We have been extremely busy getting ready for the rail startup in just a few weeks (working on all of the technology at the stations and behind the scenes that you can't see) and in pushing the Automatic Vehicle Location project forward to fruition (as I started to talk about here).

One of the exciting things we are working on is enhancing the trip planner and website to provide better information about where the vehicle you care about is and when it will arrive. The latter problem while not trivial is actually the easier of the two to report on. In fact we have recently enhanced our website to give predicted arrival times for the next 3 buses at any given stop (link). Please take a look at it and let us know what you think. Currently this information is based on scheduled arrival time, but as we turn on the Automatic Vehicle Location system we will start replacing scheduled time with estimated time (based on the present location of the vehicle and its latest speed).

The trickier bit is if we should, and how we should display the real-time location of our vehicles once the AVL system is installed. The advantage to displaying the latest location of all of our fixed route vehicles is that individual riders can figure out which vehicle will best meet their needs and it greatly improves the transparency of the system. The down side to displaying this information is that people will count on the data being precise and as everyone should be aware of by now, technology is not always as accurate as we would like (think airplane arrival times or medical billing :-)). What we don't want to happen is to put information out there that a specific bus is 3 blocks away when it is really 1 block away. People will act on the information in front of them and may miss a bus they wanted. This is not what we want to accomplish with AVL.

I think the key is to display the information in a way that quickly indicates how precise and how reliable it really is. All AVL systems have to pick a frequency of vehicle location updates. For bandwidth and communication cost reasons it is impossible to query the bus and train vehicle every second to know where it is. Practically there is little value in querying a bus every second for its location when it is moving at 5 miles per hour. Conversely it is bad to query a train at 5 minute intervals when it is moving at 60 miles per hour (the stated location will be up to 5 miles away from the true location of the train). For this reason our system will attempt to balance the frequency with the velocity of the vehicles and find a happy medium. But as with all things used by many people, it will not be possible to please everyone with the compromise we reach.

Given this challenge of frequency and real-time accuracy we are left with the issue of how to display the information in a meaningful and non-misleading manner. I pose this challenge to the Austin community as I have yet to find any transit agencies with AVL systems that seem to have solved this conundrum perfectly. For your consideration, here are some of the agencies we have found with AVL that are attempting to visually display the most recent location of their bus fleets. You be the judge and let us know what you think works best.
King County Washington Note: Shows last time the vehicle was querried
Chicago Transit Authority Note: Nice display of Google base map and option to pick routes
Next Bus Note: This is a private company that integrates the approach for many agencies

There may be others, and we would love to hear about them, but we would really like to hear your thoughts on this matter.